[Sync] ModelTypeStore factory shouldn't require valid PSS to function correctly

ios/chrome/browser/sync/ios_chrome_profile_sync_service_factory.cc

Index: ios/chrome/browser/sync/ios_chrome_profile_sync_service_factory.cc
diff --git a/ios/chrome/browser/sync/ios_chrome_profile_sync_service_factory.cc b/ios/chrome/browser/sync/ios_chrome_profile_sync_service_factory.cc
index dd239c2663fd8bf54f8374ae060eab8ae1dc73f7..994243d576f22b8c6387eb121bcf6dd7f69b4451 100644
--- a/ios/chrome/browser/sync/ios_chrome_profile_sync_service_factory.cc
+++ b/ios/chrome/browser/sync/ios_chrome_profile_sync_service_factory.cc
@@ -142,11 +142,6 @@ IOSChromeProfileSyncServiceFactory::BuildServiceInstanceFor(
   init_params.url_request_context = browser_state->GetRequestContext();
   init_params.debug_identifier = browser_state->GetDebugName();
   init_params.channel = ::GetChannel();
-  base::SequencedWorkerPool* blocking_pool = web::WebThread::GetBlockingPool();
-  init_params.blocking_task_runner =
-      blocking_pool->GetSequencedTaskRunnerWithShutdownBehavior(
-          blocking_pool->GetSequenceToken(),
-          base::SequencedWorkerPool::SKIP_ON_SHUTDOWN);
 
   auto pss = base::MakeUnique<ProfileSyncService>(std::move(init_params));